CONIFER

any member of the division Coniferophyta, living and fossil gymnospermous plants that usually have needle-shaped, evergreen leaves and seeds attached to the scales of a woody, bracted cone. Three English namescedar, cypress, and pineare each applied to unrelated kinds of conifers. Among living gymnosperm divisions, the coniferophytes show little similarity to the Cycadophyta and Gnetophyta but share several vegetative and reproductive traits with the Ginkgophyta. Coniferophytes are most abundant in cool temperate and boreal regions, where they are important timber trees and ornamentals, but they are most diverse in warmer areas, including tropical mountains. James Emory Eckenwalder any member of the order Coniferales, woody plants that bear their seeds and pollen on separate, cone-shaped structures of hard or papery scales arranged in spirals or whorls around an axis. This arrangement of a naked, exposed seed is in contrast with the angiosperms, the seeds of which are surrounded by a maturing ovule. The conifers constitute the largest division of gymnospermous plants, with about 50 genera and more than 550 species. Most of them are evergreen, upright trees and shrubs, although some lose their leaves annually and others grow to less than 1 foot (30 cm) in height. Conifers grow throughout the world, except for Antarctica, and prefer temperate climate zones. Ten genera are common in both the Old and New Worldsfirs (Abies), incense cedars (Calocedrus), Lawson and Nootka cypresses (Chamaecyparis), cypresses (Cupressus), junipers (Juniperus), larches (Larix), pines (Pinus), Douglas firs (Pseudotsuga), white and western red cedars (Thuja), and hemlocks (Tsuga). There are also coniferous genera that are limited in geographic distribution. For example, cedars (Cedrus) now grow naturally only in Eurasia and North Africa, plum yews (Cephalotaxus) from Korea to India, Cryptomeria in China and Japan, Callitris in Tasmania and Australia, and the dawn redwood (Metasequoia) in China. The podocarps (Podocarpus species) originated in Australia and New Zealand but have spread to Africa, East Asia, South America, Mexico, and the Caribbean. Among the smallest conifers is Dacrydium laxifolium of New Zealand, which has been known to reach maturity while achieving a height of only 8 cm (3 inches). Many others creep or trail along the ground, but the tallest, the redwoods (Sequoia sempervirens) of California and Oregon in the United States, may grow to more than 110 m (360 feet) in height. The swamp cypress (Taxodium distichum) and some species of Chamaecyparis and Cryptomeria are supported by massive buttresses, and others have radiating roots. The oldest known plants are the bristlecone pines (Pinus aristata) of California and Nevada, one estimated to be almost 5,000 years old. The conifers supply softwood timber used for general construction, mine timbers, fence posts, poles, boxes and crates, and other articles, as well as pulpwood for paper. Coniferous wood is also used as fuel and in the manufacture of cellulose products, plywood, and veneers. The trees are the source of resins, volatile oils, turpentine, tars, and pharmaceuticals. The most valuable softwood tree of North America is the Douglas fir (Pseudotsuga menziesii), which grows from British Columbia, Canada, south to California in extensive forests that include a variety of other timber conifers (especially Pinus species). A few of these trees can send up new shoots from stumps after they are cut, but most conifers are unable to sprout after logging. A considerable extent of the forested areas of the Pacific Northwest, therefore, is managed and harvested on a continuous-yield basis, as are the coniferous forests of Finland, Norway, and Sweden. In the Southern Hemisphere, conifers are scattered among hardwood forests or stand in isolated patches. The main sources of timber among them are the kauri (Agathis australis), rimu (Dacrydium cupressinum), several of the podocarps, and Araucaria, Austrocedrus, and Fitzroya species. Coniferous trees are harmed by violent storms, fires, and human disturbances of the environment such as stream diversion, wasteful logging, and air pollution. Insects and fungi also present dangers, such as the white-pine blister rust in North America. Conifers produce undifferentiated male and female reproductive cells (microsporocytes and megasporocytes, respectively) on conelike structures called strobili. The male cones (or microstrobili) and female cones (or megastrobili) are usually borne on the same tree, although some species produce the two types of cones on separate trees. Each cone consists of a number of scales arranged in a spiral or whorl around a central axis. In the male cones, each scale bears two pollen sacs on its undersurface. Megasporocytes and microsporocytes undergo meiosis to produce megaspores and microspores (or pollen grains), respectively. Megaspores are borne in ovules on the surfaces of the scales of the female cones. When the female cones spread their scales in spring, the megaspores are pollinated by pollen grains from the male cones that have been dispersed by the wind. After pollination, the microspores and megaspores further develop into male and female gametophytes, respectively. The latter contains the egg cell nuclei. The female gametophyte is fertilized, and its surrounding integument develops into a seed coat. The seeds may be shed soon after maturity, may remain inside the cones on the tree for several to many years, or, as in most conifers, may be shed at the end of the summer in which fertilization occurs. Seeds dropped in fall lie dormant through the winter, with about 20 percent able to germinate the next spring. Only a small percentage of seedlings live through their first summer, most of them succumbing to drought, excessive heat, browsing animals, or insect and fungus attack. Many coniferous seedlings develop a strong taproot that is retained throughout the life of the tree. Those that grow in waterlogged soil and others, however, send out lateral roots, and the taproot dies. All conifers develop branched, short roots that absorb nutrients. Conifer leaves are specialized photosynthetic organs. The characteristic features of their structure minimize water loss. The stomates (pores that provide for gas exchange) are arranged in twos along either side of the single vein and are separated from direct contact with the dry air. A protective waxy cuticle makes the leaves waterproof. Although a variety of shapes do exist for conifers' leaves, they generally have a reduced surface area in order to minimize water loss. Especially in the pines, firs, and spruces, the leaves are long and stiff and are commonly referred to as needles. Cypresses, cedars, and others, however, have smaller, scalelike leaves attached along much of their length to the twig. Phyllocladus carries on photosynthesis in flattened branchlets, its true leaves falling soon after they appear. The leaves of most podocarps, of some Araucaria species, and of the plum yews and Cunninghamia are intermediate between scales and needles. Conifers first appear in the geologic record toward the end of the Carboniferous Period (about 286 million years ago). The modern families of conifers began to appear in the Mesozoic Era (245 million to 66.4 million years ago). Members of the conifers were the dominant type of vegetation just before the advent of the angiosperms. Additional reading For information on conifers, see Gerd Krssmann, Manual of Cultivated Conifers, 2nd rev. ed. (1985; originally published in German, 1983), an extensively illustrated account of cultivars and species of conifers used in gardens; D.M. van Gelderen and J.R.P. van Hoey Smith, Conifers (1986), a pictorial work complementing Krssmann's book with colour photographs; N.T. Mirov, The Genus Pinus (1967), a thorough treatment of all aspects of the biology of the many species of this important temperate genus; George S. Allen and John N. Owens, The Life History of Douglas Fir (1972), a detailed description of the reproductive cycle of the conifer; Rudolf Florin, Evolution in Cordaites and Conifers, Acta Horti Bergiani 15(11):286388 (1951), a summary of the definitive research on the evolution of seed cones in coniferophytes, and The Distribution of Conifer and Taxad Genera in Time and Space, Acta Horti Bergiani 20(4):122312 (1963), an important survey, with thorough maps of distributions of living and fossil coniferophytes; Charles B. Beck (ed.), Origin and Evolution of Gymnosperms (1988), a collection of studies of fossil conifers with important discussions of early species; J.A. Hart, A Cladistic Analysis of Conifers: Preliminary Results, Journal of the Arnold Arboretum 68:269307 (July 1987), a new approach to discovering relationships among conifer genera; and J.E. Eckenwalder, Re-evaluation of Cupressaceae and Taxodiaceae: A Proposed Merger, Madroo 23(5):237256 (1976), an original look at family relationships among extant conifers.